Medical treatment of certain illnesses requires continuous drug infusion into various body compartments, such as subcutaneous and intravenous injections. Diabetes mellitus (DM) patients, for example, require the administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory portable insulin infusion pumps have emerged as a superior alternative to multiple daily syringe injections of insulin for Type 1 (Diabetes Medicine 2006; 23(2):141-7) and Type 2 (Diabetes Metab 2007 Apr. 30, Diabetes Obes Metab 2007 Jun. 26) diabetes patients. These pumps, which deliver insulin at a continuous basal rate, as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses according to individual prescription, since an overdose or underdose of insulin could be fatal.
The first generation of portable insulin pumps refers to a “pager-like” device with a reservoir contained within a housing. A long tube is provided for delivering insulin from the pump attached to a patient's belt to a remote insertion site. The reservoir, delivery tube and the hypodermic cannula altogether constitute an “infusion set”. The recommended time for replacing an infusion set is every 2-3 days to avoid local infection at the cannula insertion site. Most users, however, extend this period until the reservoir is empty, sometimes up to 7 days. Examples of such devices are disclosed in U.S. Pat. Nos. 3,631,847, 3,771,694, 4,657,486, and 4,544,369. These devices represent a significant improvement over multiple daily injections but suffer from major drawbacks, including large size, heavy weight and long tubing. The size and weight of these devices is primarily attributable to the size and number of batteries (i.e., AA or AAA-type) employed in the devices for supplying the required high energy demand of the motor, screen, alarms, and other components which consume energy.
These bulky devices with long tubes are uncomfortable and are rejected by the majority of users because they interfere with daily activities, e.g., walking, running, and sports. To avoid the tubing limitations, a second generation concept was proposed, directed to a remote controlled skin adherable device with a housing having a bottom surface adapted to be in contact with the patient's skin, with a reservoir contained within the housing, and with an injection needle adapted for fluid communication with the reservoir. These skin adherable devices are designed for replacement every 2-3 days similarly to the currently available pump infusion sets. Most patients, however, prefer to extend this period until the reservoir is empty. This concept is discussed in U.S. Pat. Nos. 4,498,843, 5,957,895, 6,589,229, 6,740,059, 6,723,072, and 6,485,461.
These second generation skin adherable devices still have at least two major drawbacks:                The entire device should be disposed every 3 days including all expensive components (e.g., electronics, driving mechanism).        The device is still heavy and bulky, which is exceptionally important drawback because the device should be directly attached to the patient's skin and remain in place for at least 3 days. The main reason for the large size and heavy weight is the size and number of batteries (e.g., AA, AAA or button-type) that supply energy to the motor, alarms, and maintain a communication link between the skin adherable device and the remote control unit. For example, the voltage required by many of the low voltage controllers and motors is 3 Volts, while the output of the batteries is less than 1.6 Volts.        
In U.S. Pat. No. 7,144,384 to Gorman et al., assigned to Insulet Corporation, a skin adherable device is disclosed. The patent discusses that a large portion of the device is occupied by four silver-oxide button batteries positioned perpendicular to the longitudinal axis of the device, making the device thick (18 mm) and bulky. Moreover, due to high energy consumption, such batteries typically last only 3 days, forcing the user to dispose of the entire device every 3 days.
A third generation skin adherable device was devised to increase patient customization. An example of such a device is described in the co-owned, co-pending U.S. patent application Ser. No. 11/397,115 and International Patent Application No. PCT/IL06/001276. This third generation device contains a remote control unit and a skin adherable patch unit (also referred to as “dispensing patch unit”) that includes two parts:                Reusable part—containing the metering portion, electronics, and other relatively expensive components.        Disposable part—containing the reservoir and in some embodiments, batteries. A tube delivers the fluid from the reservoir to an exit port that contains a connecting lumen.        
This concept provides a cost-effective skin adherable device and allows for a diversity of features, including various reservoir sizes and various needle and cannula types.
In the co-owned, co-pending U.S. patent application Ser. No. 12/004,837 and International Patent Application No. PCT/IL2007/001578, a fourth generation device is disclosed. This device is configured as a patch that can be disconnected and reconnected to a skin adherable cradle unit. The patch can be remotely controlled or can be operated by buttons that are located on the patch as disclosed in the co-pending, co-owned U.S. Provisional Patent Application No. 60/961,527. In this configuration, the user can deliver a required bolus dose by repetitive button pressing according to a predetermined dose per button press (“Bolus buttons”).
The co-owned, co-pending U.S. patent application Ser. No. 11/706,606, the disclosure of which is incorporated herein by reference in its entirety, discloses a device that contains a dispensing patch unit and an analyte sensing means (e.g., sensor). This dual function device has the same configuration that was outlined above and can also be disconnected and reconnected at the patient's discretion.
Both third and fourth generation devices may use a single, small-sized battery. An example of such a battery is a zinc-air battery, as disclosed in co-pending, co-owned U.S. Provisional Application No. 60/961,484. These batteries have many advantages, including low weight, small size, low cost, long shelf lives, high specific energy and high stability. However, such batteries have a limited amount of stored energy of about 0.3 W·h, while a single use zinc-carbon AA battery has stored energy of about 1.2 W·h. AAA batteries, however, are more than ten times larger and heavier than zinc-air batteries. Therefore, in order to enable employment of a small size power source, which has limited stored energy, the energy consumption of the electrical components of the dispensing patch should be reduced, especially the energy consumption of the motor, which is the primary energy consumer.
The motor requires a substantial amount of energy for its operation: a current of about 500 mA and voltage of about 3 Volts, i.e., 1.5 Watts of electrical power. The power output of a zinc-air battery provides an electrical current of 10 mA and voltage of about 1.2 Volts, i.e., 0.012 Watts of electrical power. To provide the 3 Volts required by the motor and the CPU from a battery output of 1.2 Volts, a DC-DC step-up converter is used. The current requirements are provided by a pulsed power method, i.e., accumulating energy over a relatively long period of time and releasing it very quickly, thereby increasing the instantaneously supplied power. As such, the pulsed method is based on generating periodic pulses of high power.
It is, therefore, essential that the pulses' parameters (e.g., duty cycle, pulse duration, width and amplitude) comply with the electromechanical properties of the motor (e.g., load, torque friction). This can be carried out, for example, by changing pulse duration according to the load on the motor, as discussed in U.S. Pat. No. 5,774,426 to Mai Xuan Tu et al. The electrical load on the motor is measured to determined missed steps of the motor (i.e., momentary failure of the motor). The energy supply to the motor is increased upon detection of the missed steps. Unfortunately, this invention is applicable only to a single phase step motor and it may require several iterations (including additional missed steps of the motor and loss of energy) prior to actual supplying energy sufficient to rotate the motor.
Another method to control the motor electronically is based on changing the duty cycle according to energy stored in an implanted infusion device power source, as discussed in U.S. Pat. No. 7,122,026 to Rogers et al. The duty cycle is increased to compensate for power source depletion. Yet, some energy supply devices (e.g., zinc-air batteries) maintain nearly constant power supply even when depleted. Thus, applying this method would result in unnecessary energy consumption. This method also ignores other mechanical factors associated with the motor's operation, such as inertia and load.